Process of making artificial silk



May 7, 1935. H. G. STONE 2,000,047

I PROCESS OF MAKING ARTIFICIAL SILK Filed Aug. 29, 1951 lierbfliSione,

amnion Patented May 7, 1935 UNITED STATES PROCESS OF MAKING ARTIFICIAL SILK Herbert G. Stone, Kingsport, Tenn., assignor to Eastman Kodak Company, Rochester, N. Y., a. corporation of New York Application August 29, 1931, Serial No. 560,191

Claims.

The present invention relates to the evaporative spinning of artificial silk from solutions of organic derivatives of cellulose in volatile solvents, in which the solution is projected from a 5 higher to a lower temperature in the formin of the filament.

It has been previously known to regulate the temperature of aspinning solution by maintaining it at a certain temperature entirely independent of the heating effect of the hot air in the spinning cabinet, prior to forcing it thru the orifice or spinneret into the spinning cabinet. The advantage in that process was merely to assure uniform results by having the conditions including the temperature of the spinning solution exactly the same, each time and instance in which the spinning is carried out. However, it has never been previously recognized that if artificial silk is produced from a solution of an organic derivative of cellulose by projecting it from a higher temperature environment to an evaporative atmosphere of lower temperature that filaments of improved properties may be produced.

95 I have found that when solutions of organic derivatives of cellulose in volatile solvents are first subjected to an elevated temperature and forced thru a spinneret into an evaporative atmosphere of a lower temperature that filaments are consistently formed of approximately round cross-section in contrast to the filaments ordinarily produced in silk spinning processes in which the filaments formed exhibit an, elliptical shape. Obviously filaments of such latter shape and of non-uniform cross-sectional area may wear through and break much sooner than round or nearly round filaments of uniform cross-section, so that the life of goods or fabrics produced with round threads such as are produced according to the applicants process will be longer than that of fabrics produced from non-uniform filaments of more or less elliptical cross-section. Also as round threads present less exterior surface than threads of elliptical crosssection, a smaller proportion of the cellulose derivative will be exposed to surrounding influences which might deteriorate the exposed portion of the thread, than would be the case with threads :01 a flattened nature. Round threads also present distinct advantages in weaving.

I am of the opinion that the reason the filaments formed according to my process are more nearly round than those formed in other processes is that the filaments according to my process form and set more quickly so that they the surroundings.

are less influenced by air currents, gravity or other factors which might have some effect upon the filament before it has set. This explanation however is present merely to assist in understanding the advantages of the invention and 5 not to limit it in any respect.

I have found that the filaments produced by my process possess other desirable characteristics such for example as strength or tenacity and ability to stretch, without breaking, which 0 characteristics are regarded as valuable in yarns of this character.

I have found that various organic derivatives of cellulose and various solvents may be employed in my process, as for example solutions of cellulose acetate in acetone or other volatile solvents may be employed to produce filaments of cellulose acetate. The solutions of cellulose acetate-propionate in acetone, ethylene chloride or other volatile solvents which are suitable for the production of artificial silk such as are disclosed and claimed in Clarke and Malm application Serial No. 550,203 may be utilized for the production of filaments according to my process.

My process is eminently suited for the production of filaments of artificial silk from solutions in which cellulose acetate is dissolved in ethylene chloride at elevated temperatures such as is disclosed and claimed in the Staud and Minsk'application Serial No. 553,698. 30

The accompanying diagrammatic drawing illustrates by way of example one form of 'ap-' paratus in which my process may be embodied.

Figure 1 is aside elevation of a unit of a spinning machine which may be employed in 35 producing artificial silk according to my process.

Figure 2 is a section at right angles to the view shown in Figure 1, taken along the line 2-2 of that figure.

The pipe or manifold l supplies the solution or dope of the cellulose derivative to the filamenting apparatus by means of the valve 2 and the pump 3. The dope or solution passes thru a candle filter 4 which is enclosed by a chamber 5 so as to segregate this portion of the spinning apparatus from the balance of the cabinet so that a zone of elevated temperature may be maintained independent of the temperatures of The walls of the chamber 5 may be of any suitable heat-insulating material and obviously, other things being equal, the less susceptible a material is to the conduction of heat the more suitable it is to be employed partly or wholly in the construction of the walls of chamber 5. r

In the drawing, coils 6 are provided in the chamber 5 for the passage of a hot liquid such as water or steam to heat the chamber 5 and the candle filter i. If desired a liquid may be placed in the chamber 5, surrounding the candle filter 4 and the coils 6 to facilitate the uniform transmission of heat from the coils to the filter and the uniform maintenance of temperature. Other well known heating means such as by electrical heating coils, or the like, may be employed instead of the heating coils shownin the drawing; however, heating by means of a flame such as of gas is unsuitable due to the infiammability of the volatile solvents usually employed in silk spinning and due to the dimculty of regulating the temperature of the filter when direct open flame heating is employed;

The candle filters is connected with a spinnerette T to form the dope as it comes from the candle filter into filaments of a desired size and deliver them into the evaporative atmosphere present in the spinning cabinet 9. The cabinet 9 is provided with an air inlet 9 at its lower end in which is located a steam pipe I8 with heat dissipating fins 5?, which heats the incoming air. The solvent laden air in the upper portion of the cabinet may be removed thru the outlet 8 which leads to a solvent recovery apparatus, the outlet 8 being preferably located a little below the top of the spinning cabinet.

When the hot dope is forced thru the spinneret 1 into the dead zone and passes, into the current of heated air, the solvent evaporates from the formed filaments, so that they set quickly, leaving threads of artificial silk. The thread passes over the guide roll i l (or ii desired a fixed guide may be employed) and out of a small aperture in the cabinet to the draw roll I2, from whence it is conducted to the spinning pot or bobbin i5, through the guide is to assure uniform winding of the thread.

The bobbin may be rotated by means of a motor or a belt which may also be employed for reciprocating the guide [4 in any suitable manner desired.

The drawing and description given herein is merely illustrative and various modifications and alterations may be made as desired by the individual operator, for example instead of employe ing a spinning pot and roll winding as illustrated, any other known method such as cap spinning may be employed for the collecting of the thread after its formation.

The height of the spinning cabinet thru which an evaporative current of heated air is passed may be varied according to the judgment ofthe individual operator. A longer cabinet will take up more space and will usually be more expensive to install than a shorter cabinet but, on the other hand a spinning cabinet of greater height will allow more lineal speed in filamenting than one of less length. For example a spinning cabinet having a length of 12-18 .feet which is commonly employed in spinning artificial silk will be preferred for most purposes and will be found quite satisfactory and of large capacity. Spinning chambers '12 it. high allow a spinning speed of about 180 meters per minute with an acetone solution of cellulose acetate. However if longer spinning chambers should be desired, obviously they mayv be employed, the length of the chambers above about 12 it. being merely a matter of choice depending on the inclinations of the designer. When the spinning chamber is lengthened obviously the spinning speed may be increased as the formed filament may travel faster in a longer cabinet and still be under treatment for the same amount of time as if the filament were travelling slower in a shorter cabinet. For instance if the length of the cabinet is 24 it, a spinning speed of 240-300 meters per minute may be employed with an acetone solution of cellulose acetate.

It is also preferred that the freshly formed filaments be under some tension. This stretch spinning may be accomplished by rotating the draw roll I 2 at a circumferential speed which is greater than extrusion speed at the nozzle for instance from 1.5 times to 2 times greater. For example if the extrusion speed of the spinneret is 180 meters per minute, then a draw roll of about 8 c. m. diameter may be rotated at a rate of about 1,300 B. P. M. to accomplish stretch spinning My process comprises the maintenance of the temperature of the candle filter or if no filter is employed of the pipe or passage immediately before the spinneret at a temperature substantially above that which is present in the spinning cabinet.

The following examples are given to illustrate methods which may be employed for the spinning of filaments of artificial silk from organic esters of cellulose. It is to be understood that these examples are illustrative and are intended not to limit the scope of my invention.

Example I A 20-25% solution of the ordinary commercially available hydrolyzed cellulose acetate was made up using acetone as the solvent. The solution was well filtered and pumped through the candle filter 4, located as shown in the drawing at the top of the spinning cabinet which was about 12 ft. high. Thecandle filter was maintained at a temperature of 65 C. by means of the heating coils 6. The acetone solution of cellulose acetate was forced out thru the spinneret 1 into the spinning cabinet thru which a current of air is passed at the rate of about 20 cu. ft. per minute for the forming of thread of denier. The current of air entering at the bottom of the cabinet after passing over the heating fins I! had a temperature of about 56 C. and the withdrawal temperature of the air near the top of the cabinet was approximately 48 C.

The draw roll E2 was rotated at a circumferential speed of about 1.8 times the rate of extrusion of the solution thru the spinneret. A cellulose acetate silk of 150 denier and uniform, round cross section resulted and was wound on the bobbin l5 by means of the apparatus shown.

. Example 11 A cellulose acetate-propionate having a propionyl content of about 20% was dissolved in acetone to form about a 26% solution. This solution had a viscosity of 232 seconds and.

thru the cabinet.

The solution was extruded thru the spinneret 1 into the evaporative atmosphere of the spinning cabinet, forming filaments which took the course illustrated in Figure 1 of the drawing. In this example a thread of 150 denier was produced in which case the air was passed thru the spinning cabinet at the rate of 20 cu. ft. per minute. A cellulose acetate-propionate thread is obtained having a round and uniform appearance.

Obviously if lower temperatures are employed in the spinning cabinet, the temperature of the candle filter may also be lower than given in the above example and conversely when the air in the spinning cabinet is at a higher temperature, the candle filter mustbe maintained above the temperature of the spinning cabinet according to my invention. Temperature will naturally be varied in the carrying out of my invention according to the conditions of each individual example.

For instance if a more volatile solvent is employed the temperatures need not necessarily be as high for successful spinning as with the less volatile solvents, the volatility of the solvent employed being one of the determining factors in the temperatures to be employed. The variation of temperatures in my invention however is a matter of technique and it may be regulated as desired by individuals skilled in the silk spinning art.

For most purposes, however, candle filter temperatures above 60 C. will be employed in the carrying out of my invention and in the majority of cases a candle filter temperature of 60-70 C. will be satisfactory. In most cases the heated air introduced at the bottom of the chamber will be from about 50-S0 C. nevertheless when this air has passed thru a spinning cabinet especially of the narrow variety such as most of them are, it will have lost several degrees of heat by dissipation thru the walls of the cabinet and by evaporation of the cellulose derivative solvent so that at the top of the cabinet it will have a temperature of from about 5-l0 C. less than at the bottom of the cabinet. Thus it may be seen that even if the heated air entering at the bottom of the spinning cabinet should be at as high a temperature as the candle filter, which will not usually be the case, the cellulose derivative solution upon filamenting under those conditions will pass from a higher temperature to the lower temperature which is present at the top of the spinning cabinet. As the chamber containing the candle filter is thoroughly insulated from the spinning cabinet there will be no appreciable interchange of heat so that the differenoe in temperature between the top of the spinning cabinet and the candle filter will be maintained.

I claim as my invention:

1. The process of making artificial silk by the dry spinning method which comprises extruding a solution of an organic ester of cellulose in a volatile solvent in the form of a filament into a zone of substantially immobile evaporative atmosphere and then into a current of evaporative medium of progressively higher temperatures with progress of the filament therethrough and all points of which are maintained above room temperature, but below the decomposition temperature of the ester, said solution being heated immediately prior to filamenting to a temperature higher than that of any portion of the evaporative medium, but not substantially above approximately 70 C.

2. The process of making artificial silk by the dry spinning method which comprises extruding a solution of an organic ester of cellulose in a volatile solvent in the form of a filament into a zone of substantially immobile evaporative atmosphere and. then into a current of evaporative medium of progressively higher temperatures in the direction of travel of the filaments therethroughwithin the range of 40 to 60 C., said solution being heated immediately prior to filamenting to a temperature higher than any portion of the evaporative medium, but not substantially above approximately 70 C.

3. The process of making artificial silk by the dry spinning method which comprises passing a heated solution of an organic ester of cellulose in a volatile solvent through a spinneret, whereby filaments are formed, conducting the filaments through a zone of substantially immobile evaporative medium, and then through a current of evaporative medium heated to a temperature above room temperature but below the decomposition temperature of the ester, said solution being heated immediately prior to filamenting to a temperature higher than any portion of the evaporative medium, but not substantially above approximately 70 C.

4. The process of making artificial silk by the dry spinning method which comprises passing a heated solution of an organic ester of cellulose in a volatile solvent through a spinneret, whereby filaments are formed, conducting the filaments through a zone of substantially immobile evaporative medium, and then through a current of evaporative medium having a temperature of 40-60 C., said solution being heated to a temperature higher than any portion of the current of evaporative medium but not substantially above approximately 70 C.

5. The process of making artificial silk by the dry spinning method which comprises passing a heated solution of cellulose acetate in a volatile solvent through a spinneret, whereby the filaments are formed, conducting the filaments through a zone of substantially immobile evaporative medium and then through a current of evaporative medium having a temperature of from 40-60 C., said solution being heated to a temperature of approximately 65 C.

HERBERT G. STONE. 

